A magnetic recording medium such as a magnetic tape basically comprises a support such as a polyester film and a coated film (i.e., a magnetic recording layer, hereinafter referred to as "a magnetic layer") coated thereon comprising a coating solution containing ferromagnetic fine particles such as .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, modified iron oxides thereof, or CrO.sub.2, and a binder of thermoplastic resins, such as a vinyl chloride/vinyl acetate copolymer resin, a vinyl chloride/vinylidene chloride copolymer resin, cellulose type resins, acetal resins, urethane resins, or an acrylonitrile/butadiene copolymer resin, alone or in combination.
Recently, higher recording density and higher reproduced outputs for a short wave length recording have been required for various magnetic recording media, and high efficiency media are desired. In order to satisfy the above requirements and to improve the electromagnetic properties of the magnetic recording medium, not only the surface of the support but also the surfaces of the magnetic layer and a backing layer have been made smoother, and the magnetic recording medium, particularly the magnetic layer and the backing layer, have been made thinner.
Such a magnetic recording medium having an extremely thin magnetic layer and backing layer provided on the smooth surface of a support has poor wear resistance in each layer, poor surface properties, and poor magnetic properties of the magnetic layer such as a residual flux density or a squareness ratio. Further, the magnetic layer is readily damaged and powder-dropping occurs, resulting in staining the parts of the running system of the magnetic recording apparatus and increasing dropouts due to the dusts.
Furthermore, when the above described resins are used as a binder in the magnetic layer, the magnetic layer readily causes negative static charge, resulting in significant dropouts.
When a magnetic recording medium is in the form of a thin film such as a magnetic tape or a magnetic film, it is statically charged and adheres to a magnetic recording head, and dust and contaminants adhered to the medium due to charging cause dropouts, and discharge noises occur.
In order to solve the above problems, carbon black has been added to a magnetic layer and a backing layer to improve their electroconductivity and to prevent charging. However, when carbon black is added n a large amount, problems are caused due to poor dispersibility of carbon black in each layer. That is, the surface properties of each layer and S/N of the magnetic recording medium are deteriorated. When the magnetic recording medium is a magnetic tape, unevenness on the surface of the backing layer prints through on the surface of the magnetic layer upon winding the tape, resulting in deterioration of the electromagnetic properties of the magnetic recording medium.
The binder itself in each layer can be improved so that the magnetic layer and the backing layer may resist charged, but such improvements have been insufficient to prevent charging, and the addition of carbon black is still necessary.